$A$ substance $S$ undergoes two reactions under similar reaction conditions:
$\mathop S\limits_{(2.0 \ M)} \xrightarrow{K_0} X$ (zero order)
$\mathop S\limits_{(2.0 \ M)} \xrightarrow{K_2} Y$ (second order)
The time taken for the concentration of $S$ to become half is $40 \ s$ and $10 \ s$ for the zero-order and second-order reactions,respectively. What is the value of the ratio $K_0 / K_2$?

• A
  $1$
• B
  $0.5$
• C
  $2$
• D
  $4$